Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
U.S. patent application Ser. No. 08/995,089 titled “Separators for Electrochemical Cells,” filed Dec. 19, 1997, to Carlson et al. of the common assignee, describes microporous layers as separators for use in electrochemical cells in which microporous layers comprise a microporous pseudo-boehmite layer prepared by coating and drying a boehmite sol. The microporous pseudo-boehmite separators and methods of preparing such separators are described for both free standing separators and as a separator layer coated directly onto an electrode or another layer of the cell.
When a microporous layer, such as a microporous separator layer, is coated directly onto an electrode, such as onto the cathode, the microporous separator coating may require a relatively smooth, uniform surface on the electrode and also may require a mechanically strong and flexible electrode layer. For example, for a microporous pseudo-boehmite layer having a xerogel structure, these specific electrode surface and layer properties may be required to prevent excessive stresses and subsequent cracking of the xerogel layer during drying of the pseudo-boehmite coating on the electrode surface and also during fabrication and use of electrochemical cells containing the pseudo-boehmite xerogel layer.
Besides separator-coated electrodes and electrochemical cells, a large variety of other articles comprising a microporous layer may require a relatively smooth, uniform surface on a substrate to which the microporous layer is to be applied. Also, the substrate may need to be mechanically strong and flexible. For example, for a microporous xerogel layer as used in ink jet printing media, such as described, for example, in U.S. Pat. No. 5,463,178 to Suzuki et al., such smooth, uniform, and other substrate properties may be useful in preventing excessive stresses and subsequent cracking of the xerogel layer, particularly when its thickness is above 20 microns, and also useful in providing excellent image quality. Some of the desired substrates in ink jet printing media, such as canvas, cloth, non-woven fiber substrates, and some grades of paper, have very rough and non-uniform surfaces and are difficult to coat with the microporous xerogel layers which typically provide the premium ink jet image quality. One approach to overcome the surface deficiencies of the substrate is to pre-coat the substrate with a coating layer. This approach may reduce the surface roughness and non-uniformities, but involves the expense and complexity of an additional coating step, usually does not fully eliminate the surface deficiencies, and may negatively affect the ink jet imaging, such as by interfering with the microporosity and transport of liquids between the xerogel layer and the rough but porous substrate.
In another approach that may overcome the surface deficiencies of the substrate, the ink jet ink-receptive layer may be coated on a temporary carrier layer to form an ink jet ink printing media for imaging on an ink jet printer, as, for example, described in U.S. Pat. Nos. 5,795,425 and 5,837,375, both to Brault et al. Then, as part of a two step imaging process, the ink jet media is imaged on the ink jet printer followed by lamination of the imaged ink jet ink-receptive layer to a desired substrate and removal of the temporary carrier layer from the ink jet ink-receptive layer. This approach has the disadvantage of being a two-step imaging proess where the user may obtain excellent quality in the first imaging step, but then, after the effort and expense of imaging, the quality of the second lamination step may be unacceptable. Also, this two step imaging process requires the user to have the equipment for the second lamination step. It would be advantageous to have a one step imaging process for ink jet printing on ink jet ink printing media having rough, non-uniform substrates.
A method for preparing articles, such as electrochemical cells and ink jet printing media, which can avoid the foregoing problems often encountered with preparing articles comprising a microporous layer, particularly those comprising a microporous xerogel layer, would be of great value.